In recent years, food has been treated with high pressure for the purpose of either processing, pasteurization or preservation. Pressure treatment has shown considerable promise as a new food processing technique because it can avoid problems caused by the use of conventional heat treatments such as the destruction of the nutrients and the distortion the original shape of the food product. Furthermore, the technique of high pressure processing does not alter the flavour or lessen nutritional value of the food.
The processing of food under high pressure uses a hydrostatic pressure exceeding 1,000 atmospheric pressure units. The pressure processing devices submerge material, such as food, into a pressurizing fluid sealed in a pressure container. Pressure is then applied to pressurizing fluid through, for example, pistons. This is shown, for example, in Japanese Patent Disclosures No. Heiress 3-22964 and Heisei 3-47058 in the Japanese Patent Journal.
Other methods involve a device such as a bag, diaphragm or elastic wall which is placed into a pressurizing medium and sealed in a pressure container and then pressure is applied through a secondary pressurizing medium contained in the device (for example in Japanese Patent Disclosures No. Heisei 2-89598, Heisei 3-10793 and Heisei 3-12794 in the Japanese Patent Journal). These types of containers were designed to increase the amount of pressurization, however, they require a high degree of precision manufacturing as described below.
The pressure containers used in these known pressure processing devices are constructed in such a way that a lid is used to close the opening of the container. Any gap existing between the lid and the body of the container has to be sealed with either a packing material or by some other means. This not only requires the designing of a special sealing mechanism (for example in Japanese Patent Disclosure No. Heisei 2-89877 in the Japanese Patent Journal), but it also requires a high degree of precision manufacturing in connecting the joining portions of the container body and the lid to ensure a tight seal. Without such sealing, the pressurized fluid would seep out of the container during processing. The known sealing mechanisms are often costly to manufacture and incorporate into the structure and have not heretofor proved to be entirely effective.
It is an object of the present invention to obviate or mitigate the above disadvantages.